The Single Radial Immunodiffusion (SRID) technique was adapted for testing rabies vaccines for potency. The glycoproteins from the Pitman-Moore (PM) and Flury-LEP strain of virus were purified and a sheep antiserum was prepared against the PM glycoprotein. We received antisera against the Flury-LEP and ERA-strains from NIBSC (London). The glycoprotein content of each vaccine strain tested was found to vary when tested using the different antisera and when compared to the International Reference Preparation (strain PM). However, if a homologous vaccine strain was used as the reference, the relative potency values remained constant. These data indicate that, ideally, the standardization of different strain of rabies virus vaccine requires a homologous reference for each vaccine strain. Vaccine lots containing PM, SAD and Flury-LEP strains were tested by SRID and compared to the manufacturers NIH results. These data were analyzed using correlation and regression analyses. The results showed that only the PM vaccines had a correlative relationship between the SRID and NIH tests. The results also suggest that, for the PM strain, the SRID it is a less variable means of determining vaccine potency. Future studies will concentrate on standardizing SAD and Flury-LEP vaccines and to correlate SRID results with immunogenicity studies for these vaccines. An international collaborative study was initiated and involved Control Agencies and/or manufacturers from the United Kingdom, France, Germany and Canada. Reagents for this study were prepared and provided by the Center for Biologics Evaluation and Research. As a result of this study, a proposed SRD reference preparation was identified and calibrated. We are continuing to perform the SRD on vaccine made form all three strains listed above using this reference preparation. More comparison will be needed before this test can be used to replace the mouse potency assay.